With increasing development of information industries, portable information devices such as notebook computers or personal digital assistants are widely used in many instances. In a case that a portable information device is used in a dim environment, the numbers and texts marked on the keys of the keyboard of the portable information device are usually not easily identified by a user and further hinder the user from operating the keyboards. Moreover, the user is probably suffered from vision impairment. Recently, an illuminated keyboard has been developed to be used in the dim environment in order to enhance the applications thereof. Moreover, by changing the arrangement of luminous regions, the illuminated keyboard equipped with the information device is more aesthetically-pleasing and competitive.
Generally, an illuminated keyboard is equipped with a light source and a backlight module. The fabricating cost of the illuminated keyboard is highly dependent on the cost of the light source and the cost of the backlight module. For designing an illuminated keyboard, the reduction of the fabricating cost of the illuminated keyboard is usually taken into consideration. For example, U.S. Pat. No. 7,186,936 has disclosed an electroluminescent lamp membrane switch. A top electrode layer, a bottom electrode layer and a lamp layer are formed on a membrane switch, wherein the lamp layer is arranged between the top electrode layer and the bottom electrode layer. A graphics layer is imprinted on the top electrode layer. When an external voltage is applied between the top electrode layer and the bottom electrode layer, the lamp layer emits light beams to light up the graphics layer. Since the lamp layer is stacked on the membrane switch, the light beams emitted from the lamp layer are distributed over the whole surface of the keyboard. For a purpose of locally illuminating, the illuminated keyboard needs to have additional structures to limit the luminous regions.